How to Build a Spacecraft to Save the World

Our best hope of saving the planet from a killer asteroid is a white cube the size of a washing machine that’s currently in pieces in a clean room in Maryland. When I arrived last week at the Johns Hopkins University Applied Physics Laboratory, a sprawling R&D facility where most researchers are working on government projects they can’t talk about, the spacecraft was missing two of its side panels, its ion drive was being cleaned, and its primary camera was in a refrigerator down the hall. Ordinarily, the sterile high bay would be a hive of activity with technicians in white clean suits doting on the spacecraft, but most of them were on the other side of the glass trying to get the half-built cube to talk to a massive radio dish on the other side of the country.
Next summer, that same dish in California will be the spacecraft’s main point of contact with Earth as it blitzes through the solar system on a first-of-its-kind suicide mission for NASA. The goal of the Double Asteroid Redirection Test, or DART, is to slam the cube into a small asteroid orbiting a larger asteroid 7 million miles from Earth. No one is exactly sure what will happen when the probe impacts its target. We know that the spacecraft will be obliterated. It should be able to change the asteroid’s orbit just enough to be detectable from Earth, demonstrating that this kind of strike could nudge an oncoming threat out of Earth’s way. Beyond that, everything is just an educated guess, which is exactly why NASA needs to punch an asteroid with a robot.
Astronomers have discovered about 16,000 asteroids between 140 and 1,000 meters in diameter lurking in our solar system. DART’s target, Dimorphos, is at the lower end of that spectrum, and the asteroid it orbits, Didymos, is at the larger end. If either of those asteroids were to strike Earth, it would cause a kind of regional death and destruction unparalleled by any natural disaster in history. There are more than a thousand asteroids with diameters larger than Didymos and Dimorphos combined, and if any of those were to strike Earth, it could lead to mass extinction and the collapse of civilization. The odds of this happening are extremely low, but, given the consequences, NASA and other space agencies want to be ready just in case.
The good news is that scientists think it’s possible to divert these killer asteroids if they’re detected far enough in advance. That’s not guaranteed—asteroids sneak up on Earth with distressing regularity—but there have been a lot of proposals floated over the years for how we might go about it. Arguably the most practical ideas involve blowing an asteroid up or crashing into it. But for these strategies to be effective, scientists need a better idea of how an asteroid will react. So they built DART, a deep space probe whose primary mission is to destroy itself to prove it can be done.“Everyone knows it’s possible to hit an asteroid,” says Justin Atchison, a DART mission designer at the Johns Hopkins Applied Physics Laboratory. “But there’s a big step in between saying it can be done and actually doing it. You learn a lot in that process.”
For someone tasked with building a spacecraft to save the world, Andy Rivkin, one of the DART mission’s two lead investigators, is surprisingly nonchalant about it. “An asteroid impact is not something that freaks me out at all,” he says. “We have a pretty good sense of the odds of it being a problem anytime soon. This is mostly building toward a future where eventually people may need to use this and we want to give them the tools to do that.”